Safety and Immunogenicity of Different Formulations of Monovalent Influenza A/Astrakhan/3212/2020 Like (H5N8) Virus Vaccine With AS03 Adjuvant System in Medically Stable Adults

Inclusion Criteria: Medically stable participants as established by medical history and clinical examination before entering into the study. A male or female >=18 years of age at the time of signing consent form. Participants, who, in the opinion of the investigator, can and will comply with the requirements of the protocol. Written or witnessed/thumb printed informed consent obtained from the participant prior to performance of any study specific procedure. Female participants of childbearing potential or non-childbearing potential may be enrolled in the study if specific criteria are met. Exclusion Criteria: Current diagnosis or history of autoimmune disorder(s) except hypothyroidism due to Hashimoto's thyroiditis. History of any reaction or hypersensitivity likely to be exacerbated by any component of the vaccine. Clinically significant acute or chronic pulmonary, cardiovascular, hepatic, or renal disease that appears uncontrolled or untreated, as determined by history or physical examination. Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history, physical examination, or abnormalities in screening blood tests. Recurrent history of or uncontrolled neurological disorders or seizures. History of Guillain-Barré syndrome. Diagnosed with cancer, or treatment for cancer within 3 years. Persons with a history of cancer who are disease-free without treatment for 3 years or more are eligible. Persons with a history of histologically confirmed basal cell carcinoma of the skin successfully treated with local excision only, are accepted and are eligible, but other histologic types of skin cancer are exclusionary. Women who are disease-free 3 years or more after treatment for breast cancer and receiving long-term prophylaxis are eligible. Documented human immunodeficiency virus-positive participants. Bedridden participants. Personal or family history of narcolepsy. Food and Drug Administration (FDA) toxicity Grade 2, or greater, laboratory tests at Screening. Any other clinical condition that, in the opinion of the investigator, might pose additional risk to the participant due to participation in the study. Use of any investigational or non-registered product other than the study vaccine during the period beginning 30 days before the first dose of study vaccine (Day -29 to Day 1), or planned use during the entire study period. Use of public health emergency vaccines like coronavirus disease 2019 (COVID-19), Monkey pox (mpox) etc. These can be given at any time, but there should a gap of 2 - weeks before a dose of study vaccine can be given. Use of any licensed vaccines: prior to receipt of the study vaccine and continuing up to 3 weeks after receiving the dose 2 of study vaccine. Administration of long-acting immune-modifying drugs at any time during the study period. Administration of immunoglobulins and/or any blood products or plasma derivatives during the period starting 3 months before the first dose of study vaccine or planned administration during the study period. Chronic administration of immunosuppressants or other immune-modifying drugs during the period starting 3 months prior to the first vaccine dose and through the entire study period. For corticosteroids, this will mean prednisone equivalent >=20 milligrams/day for 14 days or a total of >=280 mg of prednisone equivalent dose in any 14-day period. Inhaled and topical steroids are allowed. Pregnant or lactating female. Female planning to become pregnant or planning to discontinue contraceptive precautions within 2 months after completion of the vaccination series. History of/or current drug/alcohol abuse. Any study personnel or their immediate dependents, family, or household member. Concurrently participating in another clinical study, at any time during the study period, in which the participant has been or will be exposed to an investigational or a non investigational vaccine/product.